In a fuel cell comprising a solid oxide, a cathode reduces oxygen to oxygen ions and an anode oxidizes a fuel accompanied by a release of electrons provided by the fuel. The oxidized fuel combines with the oxygen ions to counteract a resulting flow of released electrons through an external circuit. The anode is not consumed during operation of the fuel cell. Theoretically, the fuel cell can operate as long as fuel is supplied to the anode.
Electrical output depends on several factors, including the type of fuel used and the operational temperature, as well as the electrode and electrolyte components. To provide a high electrical output, new materials have been devised that can withstand high operational temperatures. Such high temperatures may not be practical for many applications, however. In addition, a combination of currently known materials results in a heavy device, which is not practical for variable load applications. Attempts to improve the performance of fuel cells include the discovery of new materials for anode, electrolyte and cathode components. Each device, however, is generally specific for a certain type of fuel.
In a metal/air battery, a cathode reduces oxygen to oxygen ions in a similar manner to a fuel cell, but the anode itself oxidizes and provides electrons which are released to an external circuit. Thus, the anode is consumed. For charge balance, the oxidized anode reacts with oxygen ions produced by the cathode. The battery does not require fuel in order to generate electricity. The battery, however, has only a defined lifetime as determined by the lifetime of the anode.
Attempts have been made to combine the attributes of a fuel cell and a battery. For example, a device may comprise separate battery and fuel cell components, thus combining the storage capacity of a battery with the longevity of fuel cells. This arrangement, however, only adds to the weight of the device.
Much effort has been made, and continues to be made, to improve the performance of fuel cells and batteries, particularly for mobile applications where lightweight components and increased power output are essential.